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This filter is great because it helps improves the view under suburban skies, where light pollution is such a bummer.
For those wanting more info on this item, this is the blurb from the Orion website:
UltraBlock™ Narrowband Light-Pollution
Dramatically Improves Views of Emission and Planetary Nebulas
The UltraBlock is the filter for deep-sky observers located at highly light-polluted sites. Blocks all forms of light pollution - mercury vapor and sodium emission bands - while passing the critical hydrogen-beta and ionized oxygen wavelengths. With an UltraBlock, emission and planetary nebulas "surface" from the washed out background sky. In dark skies, the UltraBlock also enhances the sky presence of a significant number of fainter deep-sky objects over unfiltered and wideband-filtered views.
The one for sale is the thin larger filter in the attached picture.
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